"‘Try to make the mind stay with just a single Dhamma theme—its meditation word.’ Don’t get involved with other topics at that moment. If you let it think of the texts while practicing concentration, [the mind] won’t be willing to stick just with that practice. A great deal of extraneous knowledge will interfere, disrupting the mind until everything is a turmoil, and no stillness will result."
January 1, 1970
https://en.wikiquote.org/wiki/Ajahn_Maha_Bua